Musnad Abu Ya'la al-Mawsili 154:24

Suwayd narrated to us, Yahya bin Zakariya bin Abi Za'idah narrated to us, from Dawud, from Sa'id bin Jubayr, who said: I saw Ibn Umar, and he would owe silver (dirhams), so he would give its value in gold (dinars) when it was appraised at the market rate. And he would owe gold (dinars), so he would give silver (dirhams) according to its value.